A pneumatic tire typically includes a pair of axially separated inextensible beads having at least one carcass ply extending between the two beads. The carcass ply includes axially opposite end portions each of which is turned up around a respective bead and secured thereto. Tread rubber and sidewall rubber are located axially from and radially outward of, respectively, the carcass ply.
The sidewall and bead area are portions that receive considerable attention during the tire design process. Under conditions of severe operation, the stresses in the bead area can be especially problematic, leading to separation of adjacent components. In particular, the ply turnup ends are prone to separation from adjacent structural elements of the tire. For this reason, a variety of structural design approaches have been used to manage separation of the tire elements in the bead area and the adjacent sidewall area. These design approaches typically include adding various polymeric materials within the bead area to increase strength and rigidity. In many tire bead designs, one or more fillers or apexes will be disposed between adjacent components. For instance, an apex might be positioned immediately radially outward of the bead and between the carcass main portion and the turnup portion. A second apex might be positioned between the turnup portion and the tire side wall. Many bead designs include additional elements, such as chaffers, flippers, chippers, toe guards, and clamping members, all designed to improve the durability of the bead area.
Bead area designs including the above-mentioned strengthening elements have some drawbacks, such as increased material costs as well as increased tire weight. To address these drawbacks, tire manufacturers continue to strive for reduced weight and volume characteristics, yet provide high sidewall and bead area durability. For certain tire markets, such as the radial light truck (RLT) tire market, manufacturers have made some progress in providing bead area designs with reduced weight and high durability.
For pneumatic tires used under relatively heavier loads, such as those for the radial medium truck (RMT) tire market, the volume of the various strengthening elements are typically increased to support the increased loads, thereby further increasing the material costs and weight of the tire. Consequently, as with the RLT tire market, manufacturers desire tires having reduced volume and weight characteristics that further provide high sidewall and bead area durability. Thus, there continues to be a need for tires with reduced weight and also high durability.